A two-dimensional (2D) coding phase gradient metasurface (CPGM) is proposed for radar cross section (RCS) reduction in this work. The 2D phase gradient super cell is employed to serve as the coding element. The primary pattern of the coding element will be modulated by the designed 2D phase gradient. Thus, a more flexible method of scattering manipulation will be achieved by both the 2D phase gradient and coding sequences. The specific scattering patterns of the 2D CPGM under the modulation of phase gradient and coding sequence were analyzed. A controllable backward diffusion scattering coding phase gradient metasurface was realized based on Pancharatnam–Berry phase by modulating both the phase gradient and coding sequence. Both simulated and measured results demonstrate its excellent performance on RCS reduction.

An amplitude-adjustable metasurface has been proposed to suppress the side-lobe level over an extra-wide frequency band. A polarization-selective unit cell is designed to constitute the metasurface, which can manipulate the amplitudes of the co-polarization reflection coefficients and cross-polarization transmission coefficients, while the phases remain unchanged. The amplitude of the metasurfaces is discretely Taylor-distributed. For example, two metasurfaces were designed to achieve side-lobe level suppression (SLLS), of reflected and transmitted beams, respectively. The simulations demonstrated that two metasurfaces have good performance on SLLS of reflected/transmitted beams, with approximately −20 dB SLL in a wide frequency region. It is expected that the designed amplitude-adjusted metasurfaces may find potential application in antennas and stealth techniques.

Fast coding method of metasurfaces, based on 1D coding in orthogonal directions, is proposed in this paper. For the previous designed coding metasurfaces with M × N coding sequence, all the M × N codes need to be optimized as a whole, so that the optimized efficiency and flexibility are limited. In this regard, the coding metasurfaces are achieved via only designing the 1D coding sequences in orthogonal directions, and the coding sequences in the 2D plane can be derived by a binary addition algorithm of the two coding sequences. That means, for the M × N coding sequence, the number of coding elements that need to be optimized will be reduced from M × N to M + N . Thus, a faster optimizing method for coding metasurface design will be realized. To validate the method, 16 × 16 coding metasurfaces were designed by optimizing only two 1 × 16 random coding sequences. Both the simulation and experimental results of the designed coding metasurface demonstrated the coding metasurface design method and their excellent performance on mono-static and bi-static radar cross section reduction, which provides a more efficient coding method that allows more flexible manipulation of EM waves.

A method of engineering the frequency selective structure with absorption and transmission based on spoof surface plasmon polariton (SSPP) modes is proposed and demonstrated in this paper. High-efficiency transmission can be achieved based on SSPP modes coupling. Due to the electric field enhancement effect of the coupled SSPP on the metallic blade array, high-efficiency absorption can be achieved by the high loss of the FR4 dielectric substrate. To verify this method, the absorption-transmission-integrated frequency selective structure was designed using the metallic trapezoid structure, metallic fishbone structure and FSS. The metallic trapezoid structure can absorb the low frequency electromagnetic (EM) waves and the metallic fishbone structure can absorb the high frequency EM waves. Two absorption bands are respectively in C and Ku bands. The FSS can modulate the passband characteristic of the metallic trapezoid structure and metallic fishbone structure. High-efficiency transmission can be achieved in the middle of two absorption bands. At last, the absorption-transmission-integrated frequency selective structure was fabricated and measured to verify the feasibility of this method. It can be used for the electromagnetic windows of vessels.